Statistics

The population dynamics of Patella vulgata and other limpets.

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Abstract

Useful generalisations can be made about limpet populations
in much the same way as they can about individual animals.
These generalisations can be expressed quantitatively and formed
into a framework of population dynamics. In Patella vulgata
populations a greater mean size (defined as the 50% accumulative
weight size) indicates (i) a faster growth rate, (ii) a larger
maximum size, (iii) an increased mortality rate, (iv) decreased
mean and maximum life spans, (v) an increased settlement rate,
(vi) an earlier and more rapid seasonal maturation of the gonad,
(vii) a larger number of eggs produced per female and per unit
weight, (viii) a lower radula ratio and a flatter shell at the
mean size, than would be found in a population with a smaller
mean size. The timing of sexual maturity and of sex change is
independent of these correlated features of population dynamics.
The correlations were established by the detailed study of four
populations at Mount Batten, Plymouth; and verified by experimental
alteration of the population structure and a survey of
Patella on all types of shore.
The range of Patella vulgata in S.W. Britain is limited
at the top of the shore principally by desiccation. The
penetration of sheltered conditions is determined by interaction
between the fucoids and the limpets, On exposed shores, the
lower limit is determined by competition between P. vulgata and P. aspera. There is no direct relationship between mean size
and population density (expressed as weight per occupied area).
P. vulgata is densest at the borders of the fucoid communities
on sheltered shores, at the lowest levels on moderately exposed
shores, and at the junction with the P. aspera populations on
exposed shores. P. vulgata prevents fucoids from establishing
communities on many rook surfaces, but where fucoids form dense
stands, P. vulgata is not able to settle or feed. Physical
factors do not directly limit the range of P. vulgata (except
at the top of the shore), although they mediate the competition
and interaction which decide the precise boundaries, Inside
each P. vulgata population the growth rate 3.8 limited by intraspecific
competition for the available food.